I’ve noticed some problems handling large downlinks on both v2 and v3 of TTN.
I’m testing in the AU915 region, so I don’t know if these issues apply elsewhere.
- TTN seems to accept downlinks of arbitrary size, and actually tries to send them to the gateway.
- So if you queue a maximum size downlink (say, 53 bytes at SF12 in AU915) it will send
- BUT, if there are MAC commands pending, they will be added to the packet, making it oversize
- My gateway happens to transmit the oversize packets happily, so long as they are <= 255 bytes
- But my devices reject oversized packets, for technical reasons
- Obviously this is a standards compliance issue, but the v2 stack is sunsetting, so it will resolve with a bit of time
- TTN seems to know that a maximum packet size exists, and will keep an oversize downlink queued until the DR allows it to be sent
- However, while an oversize downlink is in the queue, confirmed uplinks will not be acknowledged
- And more critically for me, the maximum sizes seem to be wrong
- At SF12/500 in AU915, I’m measuring a maximum of 28 bytes, instead of 53 bytes
- At SF7/500 in AU915, I’m measuring a maximum of 217 bytes, instead of 242 bytes